The present invention relates to a rotary anode for an X-ray tube and a method for manufacturing the same.
A rotary anode for an X-ray tube which has a large thermal capacity and a high X-ray output has been widely used for X-ray tubes in the medical field.
Generally, a material of the rotary anode for generating X-rays by electron bombardment is selected from tungsten and a tungsten alloy which have excellent resistance to a great amount of heat generated as a byproduct when the X-rays are generated. Furthermore, in order to improve a heat resistance, a rotary anode has been used in which a molybdenum layer which is thicker than a tungsten target layer is integrally formed as a heat absorbing layer on the rear surface of the target layer.
However, along with the development of X-ray techniques, a rotary anode is desired which has a greater thermal capacity and a greater resistance to either a spontaneous high load input or a continuous load.
In order to satisfy the above need, a rotary anode has been developed which comprises a graphite body which has a small specific gravity and a large heat-dissipating capacity, and a tungsten layer or a composite layer consisting of a molybdenum layer and a tungsten layer. The graphite body and the tungsten layer or the composite layer are adhered together, for example, by hot pressing. In the hot press process, the thermal expansion factor of tungsten is about 5.times.10.sup.-6 /deg., while that of graphite is about 2.times.10.sup.-6 /deg. Thus, their thermal expansion factors differ greatly, and distortion occurs in the cooling process at a vicinity of a junction between the graphite body and the target layer, resulting in cracking of the graphite body.
Even if the adhesion between the graphite body and the target layer is completely performed, the graphite body tends to be cracked by thermal stress due to high temperature when the rotary anode is mounted in the X-ray tube and receives heat by X-ray radiation.